diff --git a/cdxj_indexer/bufferiter.py b/cdxj_indexer/bufferiter.py
index ee11029..52bff53 100644
--- a/cdxj_indexer/bufferiter.py
+++ b/cdxj_indexer/bufferiter.py
@@ -91,7 +91,7 @@ def concur_req_resp(rec_1, rec_2):
 
 # ============================================================================
 def buffer_record_content(record):
-    spool = tempfile.SpooledTemporaryFile()
+    spool = tempfile.SpooledTemporaryFile(BUFF_SIZE)
     shutil.copyfileobj(record.content_stream(), spool)
     spool.seek(0)
     record.buffered_stream = spool
diff --git a/cdxj_indexer/main.py b/cdxj_indexer/main.py
index fcfe196..208a7cb 100644
--- a/cdxj_indexer/main.py
+++ b/cdxj_indexer/main.py
@@ -7,10 +7,12 @@
 import sys
 import zlib
 import hashlib
+import heapq
 
 from argparse import ArgumentParser, RawTextHelpFormatter
 from io import BytesIO
 from copy import copy
+from tempfile import NamedTemporaryFile
 
 
 from warcio.indexer import Indexer
@@ -19,7 +21,7 @@
 from warcio.archiveiterator import ArchiveIterator
 from warcio.utils import open_or_default
 
-from cdxj_indexer.bufferiter import buffering_record_iter
+from cdxj_indexer.bufferiter import buffering_record_iter, BUFF_SIZE
 
 
 # ============================================================================
@@ -61,6 +63,7 @@ def __init__(
         sort=False,
         compress=None,
         lines=DEFAULT_NUM_LINES,
+        max_sort_buff_size=None,
         data_out_name=None,
         filename=None,
         fields=None,
@@ -91,6 +94,7 @@ def __init__(
         self.dir_root = dir_root
 
         self.num_lines = lines
+        self.max_sort_buff_size = max_sort_buff_size
         self.sort = sort
         self.compress = compress
         self.data_out_name = data_out_name
@@ -203,7 +207,7 @@ def process_all(self):
                     )
 
             if self.sort:
-                fh = SortingWriter(fh)
+                fh = SortingWriter(fh, self.max_sort_buff_size)
 
             self.output = fh
 
@@ -360,22 +364,59 @@ class CDX09Indexer(CDXLegacyIndexer):
 
 # ============================================================================
 class SortingWriter:
-    def __init__(self, out):
+    MAX_SORT_BUFF_SIZE = 1024 * 1024 * 32
+
+    def __init__(self, out, max_sort_buff_size=None):
         self.out = out
         self.sortedlist = []
+        self.count = 0
+        self.max_sort_buff_size = max_sort_buff_size or self.MAX_SORT_BUFF_SIZE
+
+        self.tmp_files = []
 
     def write(self, line):
         self.sortedlist.append(line)
+        self.count += len(line)
+
+        if self.count > self.max_sort_buff_size:
+            self.tmp_files.append(self.write_to_temp())
+            self.sortedlist = []
+            self.count = 0
 
     def flush(self):
+        if not len(self.tmp_files):
+            self.sortedlist.sort()
+            self.write_to_file(self.sortedlist, self.out)
+            return
+
+        if len(self.sortedlist) > 0:
+            self.tmp_files.append(self.write_to_temp())
+            self.sortedlist = []
+            self.count = 0
+
+        open_files = [open(name, "rt", encoding="utf-8") for name in self.tmp_files]
+
+        self.write_to_file(heapq.merge(*open_files), self.out)
+
+        for out, name in zip(open_files, self.tmp_files):
+            out.close()
+            os.remove(name)
+
+    def write_to_temp(self):
         self.sortedlist.sort()
+        with NamedTemporaryFile(mode="wt", delete=False) as out:
+            self.write_to_file(self.sortedlist, out)
+
+        return out.name
+
+    def write_to_file(self, iter_, out):
         lastline = None
-        for line in self.sortedlist:
+        for line in iter_:
             if lastline != line:
-                self.out.write(line)
+                out.write(line)
             lastline = line
 
-        self.out.flush()
+        out.flush()
 
 
 # ============================================================================
diff --git a/test/test_indexer.py b/test/test_indexer.py
index 0763a61..dee7ea0 100644
--- a/test/test_indexer.py
+++ b/test/test_indexer.py
@@ -226,6 +226,7 @@ def test_warc_cdxj_compressed_2_with_digest(self):
                 compress=temp_fh,
                 data_out_name="comp_2.cdxj.gz",
                 lines=11,
+                max_sort_buff_size=1000,
                 digest_records=True,
             )